Although Japan has an increasing number of children who are learning Japanese as their second language (JSL students), relatively little is understood with regards to their acquisition of the Japanese language. Since acquisition of kanji (i.e., Chinese characters used in Japanese) is considered a critical skill for academic success at school in Japan, this study examined the reading and writing of kanji among JSL students, focusing on students who were born in Japan but raised in non-Japanese speaking homes. A set of kanji reading and writing tests were administered to 27 4th grade JSL students, and their performance was compared to that of their Japanese native-speaking (NS) counterparts. While the oral proficiency of the JSL students was found to be equivalent to that of the native speakers, there was a significant difference in kanji reading between the JSL and NS students even though no differences were found in kanji writing. An error analysis indicated that the JSL students had more missing answers, and more errors associated with meaning in kanji reading. Among the various background factors, only the frequency of reading in Japanese outside of school was found to be significantly influential over the students’ kanji reading. With respect to kanji writing, in addition to the frequency of reading in Japanese, the amount of practice of kanji writing and the frequency of reading outside of the school in the students’ first language (L1) were found to be significantly influential.